Devices and methods have throughout been developed for the efficient transfer of data messages from one distance to another. The exponential growth in the volume of data message transfer led to the development of switching, effectively allowing multiples of data messages to be delivered over common lines.
Innovation eventually led to optical networks, which are shown to be suitable for providing the required transmission bandwidth for the rapidly growing communication traffic of present day.
Switching technology has likewise progressed. Packet switching has been widely considered as a successful approach to efficiently deal with the problem of transporting bursty data traffic. In packet switched networks, data streams are broken up into small packets of data. These small packets are multiplexed together with packets from other data streams inside a network. The packets are exchanged inside the network based on their destinations. To facilitate switching, a packet header is added to the body, i.e. “payload”, in each packet. The header carries address information, for example, the destination address or the address of the next node in the path. The intermediate nodes read the header and determine where to forward the packet based on the information contained in the header. At the destination, packets belonging to a particular stream are received and the data stream is put back together. The predominant example of a packet-switched network is the Internet, which uses the Internet Protocol (IP) to route packets from their source to their destination. Packet switching may be one of the most important data transportation methods for furthering optical networks.
One problem in implementing a packet switched optical network is the difficulty of guaranteeing high bandwidth utilization, i.e., packet exchange rate and link utilization, when the fiber transmission rate is high. In an optical network node, optical switches are the devices to exchange packets between inputs and outputs of the node. Occasionally, optical switches require reconfiguration for the packet exchange. Although fast all-optical switching technologies have been demonstrated recently, fast optical switches with a switch reconfiguration time in nanoseconds or picoseconds range are only available in smaller sizes, such as 2×2. Large optical switches with up to a thousand ports have been demonstrated using the micro-electro-mechanical systems (MEMS) technology but the required switch reconfiguration time is in milliseconds (Kim et al. “1100×1100 part MEMS-based optical crossconnect with 4-dB maximum loss”, IEEE Photonics Technology Letters, Vol. 5, No. 11, PP. 1537-1539, 2003). Although a multi-stage approach has been commonly used to build large electrical switches from small switches, the rapid accumulation of optical loss through the stages and the high interconnection complexity make it impractical for optical switches.
In the packet transmissions, a guard time (Tg) between packets is required to prevent packets from interfering with each other. In existing packet switches, packet-by-packet switching approach is used. The Tg must be larger than the reconfiguration time (Tsw) of the switches that exchange the packets, i.e., the Tg between packets has to be sufficiently large to prevent packets from being accidentally discarded in the switch. Since no data transmission can be taken during the period of Tg, low transmission bandwidth utilization will be obtained if the Tg is large. Owing to the lack of large, fast optical switches, some approaches such as optical burst switching (OBS) tend to assume very large data packets for reasonable transmission bandwidth utilization (Qiao et al. “Optical burst switching (OBS)—a new paradigm for an optical Internet”, Journal of High Speed Networks, Vol. 8, pp 69-84, 1999.) Since one cannot lengthen the packets by too much, the switch reconfiguration time will become increasingly significant in determining the transmission bandwidth utilization, unless we can reduce the switch reconfiguration time in proportion to the increase in the fiber transmission rate, or relax the constraint imposed on the packet guard time Tg by switching fabric reconfiguration time Tsw.
It is an object of the present invention to overcome the disadvantages and problems in the prior art.